1. Field of the Invention
The present invention relates to a looper-thread feed device. It relates more particularly to a looper-thread feeding device for feeding a looper thread in an eyelet buttonhole sewing machine, the sewing machine comprising a turnable looper pedestal, a thread cutting device for cutting the looper thread, and a buttonhole cutting device; a throat plate and a thread tensioning device which tensions the looper thread being provided on the looper pedestal.
2. Description of Related Art
A looper-thread feed device of background interest is known from German Patent 11 75 535 (contained in U.S. Pat. No. 3,254,616). This known looper-thread feed device consists essentially of a throat plate which is fastened on a turnable looper pedestal of an eyelet buttonhole machine and provided with a thread clamp, the throat plate containing a narrow guide slot. The slot debouches into a needle hole contained in the throat plate, the guide slot undercutting a region of the throat plate which adjoins the needle hole. By the special arrangement of the guide slot in the throat plate, the result is obtained that the cut end of the looper thread, which has been severed by a thread cutting device after completion of a given sewing step, is guided, upon the return movement of the throat plate into the starting position for the next sewing step, into the stitch-forming region of the needle hole. In this way, in the next sewing step, the result is obtained that the end of the looper thread, fed in the manner described above, is sewn into the buttonhole welt of the buttonhole in question, as a result of which subsequent cutting of the end of the otherwise protruding looper thread is dispensed with.
A disadvantage of the known looper-thread feed device is that the throat plate, which is undercut in part by the guide slot, has a considerable reduction in cross section in the region in question so that the throat plate may be broken if struck by the sewing needle.